Borrelia burgdorferi infections in children and adolescents in Switzerland - a seroprevalence study 2023/2024 (BOBUINCA).

Background: Lyme borreliosis is one of the most prevalent tick-borne diseases in Europe. Studies on seroprevalence of Borrelia burgdorferi IgG antibodies in children are rare. The aim of this study was to determine the seroprevalence of B. burgdorferi IgG antibodies in children and adolescents residing in North-Western Switzerland and neighbouring countries.

Methods: Prospective cross-sectional observational single-centre study using left-over plasma of asymptomatic paediatric patients. Included were children aged 1-17 years living in North-Western Switzerland and bordering areas of France and Germany. Excluded were children with symptoms of Lyme borreliosis or a chronic disease possibly affecting plasma antibodies (immunodeficiency syndrome, systemic lupus erythematosus) or with such medication (e.g., intravenous immunoglobuline treatment, allogenic stem cell transplantation, immunosuppressive treatment) as well as refugees seeking asylum. IgG antibodies against B. burgdorferi were measured by ELISA and positive or borderline results by line blot. Positivity was defined as scenario 1: ELISA positive/line blot positive or borderline OR ELISA borderline/line blot positive. Scenario 2: ELISA positive or borderline/line blot positive. A multivariable logistic regression model for seropositivity was applied.

Results: 962 children were included (mean age 9.63 years, standard deviation 5.01, 54.5% males). Seroprevalence for scenario 1 was 13.3% (95% CI: 11.2-15.6) and for scenario 2 11.2% (95% CI: 9.3-13.4). Seroprevalence (scenario 1) was comparable for age groups, sex and rural versus urban residence.

Conclusion: This study shows an increased seroprevalence for B. burgdorferi in the paediatric age compared to previous childhood studies. We also found an increased risk for B. burgdorferi infection at young age.